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Professor Chris Calladine - a celebration

19 August 2002

Professor Chris Callladine FRS

A Conference on the theme "New Approaches to Structural Mechanics, Shells and Biological Structures" will be held in the Department of Engineering, University of Cambridge, on 9-11 September 2002. The conference will mark the retirement of Professor C.R. Calladine, FRS after 42 years on the teaching staff of the Department of Engineering. Former research students, collaborators, and colleagues from around the world will gather to discuss the unique contributions made by Professor Calladine and the new avenues that have been opened as a result. Around 40 lecture presentations will be given and a published volume, edited by Horace Drew and Sergio Pellegrino, will be available at the meeting. The list of contents is downloadable.

Professor Calladine, well known for his contribution to the field of structural mechanics, is considered to have made a scientific contribution outside engineering, in molecular structures, at least as significant. A scan through his publications reveals his range of expertise from 'the yielding of clay', through 'buckle propagation in submarine pipelines' to 'design requirements for the construction of bacterial flagella'.

Graphic depicting a double helix

"What would an engineer know about DNA?" once remarked an eminent biologist at Cambridge about Professor Chris Calladine. He soon proved what he did know; culminating with a book on the subject (Calladine and Drew 'Understanding DNA:the molecule and how it works.' Academic Press London 1997).

Nobel Prize Winner, Professor Aaron Klug, tells of scientific conversations with Calladine over lunch at Peterhouse about the structure of spherical viruses and the relation of their protein shells to geodesic domes. It was these conversations - the classic example of the value of college life - that led Calladine into a field far from the normal stamping grounds of engineers (certainly in the 70s). The interesting geometric features of protein assemblies were to occupy a significant part of his working life. Calladine worked on these ideas, leading to the production of a major book on the subject in 1983 ('The theory of Shell Structures' CUP 1983).

Klug also introduced him to the biological problem of the construction of bacterial flagella - the flagellum is made from a helical array of a single type of protein subunit. Calladine took a structural engineer's approach to the problem of how the various observed forms of the flagella could be derived from the same sub units and proposed that there were in fact two different forms-a prediction that proved correct. His simple mechanical model reproduced all the main aspects of the forms of bacterial flagella.

In each of the systems he studied, Calladine constructed physical models to illustrate the mechanical and geometric principles involved - leading to an interesting summation in a paper by Dr Ben Luisi of the Department of Biochemistry entitled: 'Understanding biological machines using household items' - a description of the many models that Calladine has come up with over the course of the years. Luisi summarises: "Somewhat like the best childhood toys, these models and others from Chris have inspired a lot of insight, fun and imagination that have somehow transcended far beyond their deceptively simple construction."

Professor Calladine has applied the same line of investigation to many engineering structures whose behaviour did not follow conventional wisdom. A notable example is his work on 'Tensegrity structures' (Buckminster Fuller was responsible for coining the phrase "tensegrity" which he used to describe a structure which maintains its integrity through tension.) These structures were at first thought to be "highly non-linear" by structural engineers, but Calladine showed that when the analysis had been properly formulated, they were just as linear in their response as conventional structures.

Another example of Calladine's work was his solution to a problem regarding the geometric instability of an early helium balloon. Large unmanned helium balloons provide NASA with an inexpensive means to place payloads into a space environment, and Calladine's work recently provided the basis for the design of the Long-Duration Flight Balloons, which - after several failures - were recently successfully tested by NASA.

Klug sums it up "He has the knack of picking out problems which are tractable, or which he makes tractable, by using physical insight to simplify them to their essentials and produce imaginative solutions. Coupling these with simple but powerful mathematics, he explains the phenomena quantitatively, but at the same time provides clear pictures which all can understand. We are in his debt."

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